The present invention relates generally to a master cylinder for a hydraulic brake system of an automotive vehicle. More specifically, the invention relates to a tandem piston master cylinder having a primary piston and a secondary piston in tandem relationship and arranged to independently supply the working fluid to front and rear wheel cylinders.
Brake system master cylinders having primary pistons for supplying working fluid to rear wheel cylinders and secondary pistons for supplying working fluid to the front wheel cylinders are well known. In such master cylinders, the primary piston and the secondary piston are positioned in a housing in a tandem relationship so that they can be operated cooperatively by the application of a brake pedal. As is well known with such arrangements, the load applied to the front wheels is greater than that applied to this phenomenon has been known as nose dive and can lead to locking of the rear wheels prior to locking of the front wheels and thus to skidding of the vehicle. As the result of the rear wheels locking prior to the front wheels, the vehicle tends to spin about the front wheels.
To prevent a vehicle from spinning caused by rear wheel lock, brake systems have been developed having proportioning valves in the hydraulic circuit for the rear wheel brakes. This results in increasing of the cost of the brake system and makes the hydraulic circuit for the brake system so complicated that it becomes difficult to assemble and maintain.